BRC 150 circlip vs spiral lock question

yamadog35

Member
I've got a question for those that are running or building the BRC 150 engine. I'm running this engine on a laydown enduro kart and had a recent failure where a circlip came out and caused some damage as you can imagine. Pretty much everyone in the enduro community uses spriralocks instead of traditional circlips because they tend to stay put and manage the movement of the wristpin better. The problem is I can't find a source for spiralocks because they need to be 15mm instead of the 14mm used in most all of the other engines we run. Has anyone used sprialocks in their BRC 150 and if so, where did you get them?

As a sidenote I'm using the VHM piston and the wrist pin that comes with it. I've also been using some IAME .045" circlips instead of the thinner circlips that come with the piston.
 

GoFast

Member
Hm, not sure, but you can measure the grove width & depth of the VHM piston.
I would think (for what it's worth), that VHM makes their grove wide enough for their clips, not the larger diameter IAME clips.
May have been your problem (locks not fully seated due to a too narrow grove).
Also, the grove needs to be deeper, so that the centerline of the clip is below the edge of the grove.
So good chance that your choice of using a fatter clip lead to your problem.

Spiralocks need a square bottom grove, so only use them if the groves on your piston are square bottom, or modify them so they are. I've done it.

McMaster-Carr has a good selection of Spiralocks.
 

GoFast

Member
Buttons are fine for low output 4-strokes (until you get one a little to hot, and they melt).
But you can't use them on a 2-stroke, the transfer ports will eat them, and the BRC power output is way to high, and they would melt.

Compare the output of the BRC in HP/displacement, to that of a really built VW, or lawnmower engine, and you will see.
5 hp per cubic inch of the BRC, vs. 1.5 hp for a 4-stroke.

Just put the correct clips in, or machine the piston for Spiralocks.
 

flattop1

Dawg 89
Got some good info from this thread. I never considered the need for a square groove with the spiro locks.
One thing I do not understand is. What does the horsepower have to do with it? One horsepower or fifty horsepower shouldn't affect the button at all.
The rpm maybe; if it caused a increase in temp that would be sufficient to melt the button.
Of course if the button can get into a port that won't work.
 

ZacLamb

Member
I always ran the BRC with the circlips that came with the piston. Never had one fail. Did have a VHM piston cold stick at 95 F water temp. Best piston combo I found was the vertex piston with a TiN coated ring from wiseco (about $130 for piston and ring). Had issues with the vertex ring beaking around the ring pin. If my race ready kart weight was anywhere near 350 i'd be on a BRC no question.
 

Howe17

Member
Funny, I've seen plenty of 22,000 rpm 2-stokes that stay together just fine with normal 'C-clips.
Thats nice for u but why take the chance on destroying an engine. Have you ever seen an engine loose the circlip and see the damage it does to the top end and bottom end. Maybe the gentleman who started this post could send his destroyed engine to u to repair! Rlmfao. :cool:
 

flattop1

Dawg 89
post states , not using circlip provided with piston .
Post two states where that could lead to part failure.
No response on whether the grove was actually wide enough for the circlip used only that is was wider then supplied clip.
If it is wider I can see where it would also be taller and not sit in the groove properly, thus being able to pop out.
Is there any reason not to use a spiro lock? Besides the fact they are a bear to get out.
 

GoFast

Member
Is there any reason not to use a spiro lock?
No reason than what I already stated.
That is if the grove has a round bottom, and not a square bottom.
If the groves are a round bottom, they can be machined to a square bottom.
I've done it.

Removing them isn't normally a problem, but there must be a notch on the edge of the bore,
just like a C-clip requires.
 

rainman

Premium User
Funny, I've seen plenty of 22,000 rpm 2-stokes that stay together just fine with normal 'C-clips.
I agree. That's all I used back then when I ran ICA and I still do on my Direct Drive rotary. Never had any problem with good quality c-clips.
 

yamadog35

Member
I've been traveling for work and haven't been able to get back to this post I made til now. Thanks for the input. It is always interesting to read the various opinions. I'm not an engine builder, just the consumer for many years and I'm not smart enough to know the reasons why something might work or not work. I just know in the relatively small cross section of engine builders I come into contact with in the enduro kart world they go by spiralock=good and traditional-circlip =bad. At least that's my interpretation which could be wrong. It could be more like traditional circlip="can have problems and sometimes fail" and spiralock="bullet-proof so why take a chance on the circlip". Like I said, I'm not smart enough to know so I go by what people that have a lot of experience have told me.

Having said that . . since I started this thread I've talked to Riley Will and have myself convinced to use the circlips that come with the VHM piston that we're using in the 150. Riley uses VHM pistons in other engines like his 250's and not had a problem with the provided circlips so that is what I'll do. That and I haven't found the 15mm spiralocks I would need anyway. Next up is Daytona so over that three days if all goes well we'll put somewhere between 2 to 2.5 hours running time on the engine with a lot of that at top end since about a minute to minute/twenty of each road course lap is spent on the NASCAR oval. Hoping for the best.
 

flattop1

Dawg 89
Is there any truth to the location of the circlip opening being at top or bottom?
Not 3 o'clock and nine o'clock.
Due to momentum causing it to close up at the top and bottom of the stroke.
 
Top